Oh, that's a long stay. I'm a bit envious I can't afford a 3-week stay with currents rates.I'm going from 27th of July to 18th of August ^^
As for the events, apart from Idolfest there will be the summer Harokon, Comiket, SKE handshake event and many other things. I wonder if I'll manage to visit them all or I'll have to give up on something.